The present invention relates to data storage systems and, in particular, to a method and apparatus for measuring the fly height of a head used in a disc storage system.
Disc storage systems are known in the art and are used to store information for later retrieval. Such disc storage systems include a rotating disc which carries information thereon. A transducing head (or, in some instances, a read back head) is positioned over a surface of the disc while the disc rotates at high speed. The head is carried on a slider which is designed to xe2x80x9cflyxe2x80x9d just over the surface of the rotating disc. The head may then be used to write information onto the disc or read information from the disc. Such information may be, for example, magnetically or optically encoded on the disc surface.
Increased storage density is becoming increasingly important. One technique known to increase storage density is to decrease the xe2x80x9cfly heightxe2x80x9d of the head. Fly height is defined as the distance between the disc surface and the head or slider during operation of the storage system. A reduced fly height allows information to be written or read back more precisely and such information can be stored in a smaller area (i.e., at a higher density).
Various techniques have been used in the art to measure the fly height of the head. For example, if a disc is designed to operate with a certain fly height, typically, this fly height must be measured in order to ensure that the system is operating within specification. Commonly, the fly height is measured before assembling the head and slider assemblies into disc drives. One technique to measure fly height is by measuring electrical capacitance between the head and the disc. Another common technique to measure fly height is using optical interferometry in which a transparent test disc is used to fly the slider. Light is shined through the disc onto the slider from a source on the other side of the disc. Using known techniques, the reflected light can be examined to determine fly height. U.S. Pat. No. 5,280,340, issued Jan. 18, 1994 to Lacy describes a number of such techniques for measuring fly height. Prior art techniques have also used the amplitude of the read back signal provided by a read back circuit coupled to the head to measure head fly height.
Disadvantages of the above and other known apparatus include long measurement times and the need for additional electromechanical hardware. In addition, fly height measurement systems using only the amplitude of the read back signal to measure fly height have a sensitivity that is too low for precise high speed true fly height dynamic measurements.
The present invention addresses these problems, and offers other advantages over the prior art.
Embodiments of the present invention relate to a fly height measurement scheme that utilizes a read back signal amplitude and pulse width to determine head fly height, thereby addressing the above-mentioned problems.
A system for measuring fly height of a head over a rotatable magnetic disc having a disc surface on which data is digitally stored is provided. Data is digitally stored on the disc surface by selectively polarizing portions of the disc surface into at least a first magnetic state or a second magnetic state. A read back circuit is coupled to the head. The read back circuit generates an electrical read back signal in response to the head encountering a transition between magnetic states. The system for measuring fly height includes a measurement circuit coupled to the head read back circuit to measure pulse width and amplitude of the read back signal. A calculation circuit coupled to the measurement circuit determines the fly height of the head based on the measured pulse width and amplitude of the read back signal. In addition, a method of measuring the fly height of a head by using a read back signal in a disc drive storage system is provided.